Tension bolt joint



Patented May 11, 1948 TENSION BOLT JOINT Harold W. Earhart,

Wichita, Kans., assigner to Beech Aircraft Corporation, corporation of Delaware Wichita, Kans., a

Application June 8, 1945, Serial No. 598,219

6 Claims. (Cl. 287-127) The invention here disclosed relates to what are known as tension bolt joints, in which the bolts holding the members joined together carry any tension loads to be transmitted through the joints.

In ordinary joints of this character the bolt also is forced to carry transverse loads through shear in the bolt. Such joints require close tolerance fits between mating components, that is,'between the fittings and the bolt and between the faces of- '1 the fittings to transmit transverse loads from one fitting into the bolt and from the bolt into the other fitting and compression loads from the face of one fitting to the face of the other.

These ttings are expensive due to the pre-- cision machining required to eifect the necessarily close fits and because of the precise tooling needed to hold the close tolerances on the structural components.

Also, such joints are diflicult to inspect to see.

that the proper amount of bearing is provided for transmission of compression and transverse loads. The precise iit required many times makes these joints difficult to assemble and to take apart.

Objects of the present invention are to avoidil and eliminate objections and limitations such as mentioned, existing in present day forms of tension bolt joints.

More particularly it is a purpose of the invention to provide joining means efciently transmiti ting both transverse and axial loads at the same time and through a combination of shear fastener and tension fastener arranged each to carry its proportion of design load at a strength-weight ratio providing a desired factor of safety.

Further objects of the invention are to attain simplicity and low cost in the fabrication of the mating parts and to accomplish full interchangeability of parts.

Other important objects are to provide a fastener of the type indicated particularly suited to the designing and building of aircraft.

Other desirable objects and the novel features by which all purposes of the invention are attained are set forth or will appear in the course of the following specification.

The drawing accompanying and forming part of the specification illustrates certain present em bodirnents of the invention. Structure, however, may be modified and changed as regards the immediate disclosure, all within the true intent and .broad scope of the invention as hereinafter den 'fined and claimed.

Fig. 1 in the drawing is a broken longitudinal sectional view of an embodiment of the joint ap- 2 pearing as on substantially the plane of line .of Fig. 2; Fig. 2 is'a broken sideelevation of the joint;

Fig. 3 is an enlarged cross sectional View as on lsubstantially the plane of line 3-3 of Fig. l;

. Fig. 4 is a further enlarged broken sectional.

' detan.

Fig. 5 is a broken sectional detail of a modied form of the invention.

In the drawing the fittings which vare joined tolgether and which may be two end-toend sections of a beam, strut or other structural element, are designated 1 and 8. These are finished oi with labrupt end faces of substantially the full cross sectional area of the pieces, but'such faces in .stead of being smooth or machined with nterntting parts as in prior tension bolt structures, are provided, in the form of the invention shown in Figs. 1 to 4, with relatively sharp projections or serrations 9 and intervening iiat areas or lands I0.

Specifically the serrations and intervening lands are shown provided by a sharp edged ridge extending in spiral convolutions across the end each member.

The purpose of these projections and lands is to Aeffect an automatic interlock for carrying the shear loads and full engagement for carrying compression loads across the joint. v

These results are attained by the interposition of a layer II of softer material than the faces of the fittings but of ashear strength suiiicient to transmit the transverse loads without impairment.

Forming a part of this combination is the. ten- ,sion bolt I2, designed and arranged to carry all tension loads, but free of transverse, shear load.

This bolt is shown as bearing at opposite ends on seats or shoulders I3, I4, provided in recesses I5, I6, in the opposing end portions of the fittings and as extending, in the clear, through registering Ioversize openings I1, I8 and I9, in the fittings and interposed connecting layer.

When the bolt is tightened to approximately its yield stress, the serrations will be impressed into the washer-like connecting layer or spacer of relatively softer material and this material will be forced into full contact with the flat areas be tween the serrations. This intervening layer is thus made fully capable'of carrying both shear and compression loads. The pressure applied in forcing the connecting material into fullyseated engagement on the flats serves to conne such material Abetween the 'ridgesbuildingup the shear strength in that way'.

The shear load interlock between the joint members and intervening connector may be provided by reversing the relation shown, that is, by forming grooves or indentations in the ends of the fittings, instead of projecting ridges or serrations. For some purposes the end faces may be knurled or otherwise machined to accomplish the formation of .relatively sharp points, .a .relatively sharp edgelior'la series of edges, curvedor straight, with intervening fiat areas or reliefs.

In all forms the transverse loads are transmit'- 'ted from the face of one fitting through .whatare termed the serrations, into the connecting washer and from the washer throughthe-:serrations :into the other fitting. All compression loadsare taken directly through the Washer or spacer.

In some circumstances it may be morepractical to put the serrations and lands on the Washer member and maire that member of harder'material than the opposingiaces of the fittings. This lalternative is illustrated vin :Fig -5 where the washer element is indicated at 20, of harder material. .thanthefendz faces of ,the tt-ingsvand as -having Serrat-ions: -9 :and :intervening ,-lands e H3 at oppositesidesimpressed in.andcooperatingswith tthe opposing-ends of :the fittings As another illustration the serrations or other ,elements forJfor-mingrthe.fshearnload impressions in the impression materialfmaysbeeon vseparately fformed pieces :attachedeither :tothe: faces of the fittings/forte, thefaces :of the;Washer.airfvvafen as :Instead of a single -ebolt and :washenthe joint vmay be @made `up .of ,plurality of :bolts and washers;accordingtordesign requirements.

VThe spiral-orfscrollfonm ofserration canbe inexpensi-vely l:produced and thas .many otherfadf-va-ntages. YTo :provide further interlock it imayA Vbe `intermiptedsor otherwisefvaried in configuration. 'The extent sof projection rof the ridges, points, spurs or teeth may -be relatively slight as compared =with #the ltotal `thickness vof .thee-wafer, =usually1less than-half the :thickness 1 of--the anate- -rialfsoas to avoidpossibility of completenpenetration in the event of alignment of edges .or .points at 'opposite faces -of athe material.

' The `-seats 'for-the =boltheads1=are located f far encnzgh backffi-'oin the fend'V faces for development of the full tensile-strength ofthe membersA and,

yif desired,l `nload carryingwashersmay'-beLdisposedY beneathlthedheads rfand -nuts of the bolts.

'Thefseating -of rthe ftension bolts in cavities Within the-confines or outlines of the -eonnected members and at the center of the opposing-areas provides balance Aandf otherwise Aadapts ethe invention -particularly'to ldesign and `structural problems in-aircraft.

`The 4joint is arrangedtocarry the y'full tension, compressionpandshear -loadswhich the parts are capable o`f carrying, l-and practically -vvithout .adding any .weight "Theseijoints-can Ibeiqnickly made up and, with 'the' use Vof llool: Ynuts ror equivalent such asl indicated. at 2 |,.-Fig. 111, will v.holdundergthe tensionto which they havebeen set .c up. .untilpurposely released. When released gtneparts. .can .be,.-imm.ediatelv separated. Reassemblingpis just aseasybecause, ofthere being .no need:termatchcloselyflttingaparts.

.Thettighteningofzthegjoint automaticallyinterlocksfrtheimpression material Yin 4-.tl.ie sshear vload .'snstaining :condition '.andin'slichzoperation vtends feto; correct,orcompensatejfonanmliehtzmisalignement rwhichfmay have'existed:inathegbringingA of the parts together into thei-eabutting-frelation.

The tension fastener and shear fastener portions of the connection carry their full proportions of the design load with the desired factor of safety and by their arrangement enable complete 5 and full inspection.

What is claimed is:

1. A tension bolt joint comprising members having. opposed-abutment faceal a layer of shear ,load carrying 4material between said opposed abutment faces, said members having bolt seats sin back of said abutment faces and Aregistering @vereine bolt passages extending between said seats, a .bolt having a head bearing on one seat and f a--n-utbearing on the other seat, the grip `v portion'of-the Abolt between said head and nut eX- ten'ding free of engagement through said bolt v(passage,'fsa-igiintermediate shear load carrying layer ,and the opposing abutment faces at opposite sides ofthe same varying in surface contour and having a hardness differential whereby under the tension .of the bolt, portions onthevharder sur- ;faces create counterpart interlocking im-pressions in the softer material.

2. :A tension bolt joint comprising members having opposed abutment faces, a layer offshear load carrying Amaterial .between said lopposed abutment faces, said members havingxboltseats ineback of said abutment faces andlreg-istering -oversize bolt passages extending .-betweenrsaid l-seats, aboli; having a head bearing `on .oneseat and anut bearing on the vother seat, thegrip portion of the bolt betweensaid head andfnut .extending free of engagement through said-bolt passage, said intermediate shear load .carrying layer. and the opposing .abutment .faces v.at op- ;positeesides yof the same varying insurfaoecon- :tour-Land having a hardness .differential whereby under the tension ,of the bolt, .portionsnnthe harder surfaces create counterpart'jinterlooking '.40 impressions in .the softer material, said .layer :bein-g. thei harder structure. and. having. the `impression forming portions .on.,opposite V'faces ,of -ithe `same interlocking int-the softerfabutment facesof @the joined member f3. A :tension :bolt joint .comprising .members having opposed abutment'faces, a layer Aof .shear .load carrying ymaterial :between said .fopposed abutment faces, said membershavngebolt seats in rback'of: said abutment facesand .registering oversize `boit :passages `extending between lsaid `seats, a lbolt having ahead bearing.V on'vone seat and .a nut bearing on the other seat-'fthe grip Kportion of the bolt :between said, head-andgnut l extending. 'free of engagement/.through said :blt 155 passage,said intern ediate-shearxload 4carrying :layer and .the opposing .abutmenttfacesat opposite. sides of thesame varying in :surface `con- -..-tou1'. and having ,a hardness differentiaLwhereby under the tension of the bolhftportigns `on "theyharder surfaces create counterpart interlockring :impressions -in the 4softer material, the interposed layer vbeingtlie Asofter material fandthe impression forming portions beingcarriedby the :abutment faces of the joined :members 1.4. A tensiongbolt joint V.comprising members having opposed abutment faces, a layer of Shear load vcarrying material between ,said `opposed abutmentY faces, said 1 members-having :bolt pseats pin vba-clrof-gsaid abutment faces and registering oversize .bolt passages extending-@bet-,Ween@said seats, a bolt having-.a head bearing l.911elle.Seat and afnut `bearing ontheother seat,.th e jip portion of the bolt between Asaidjhead,aintl-,nut -.extendi;ns free Vlof engagement: throuehaidbolt 75 @passage-:said intermediatershear,ileadafearnins layer and the opposing abutment faces at opposite sides of the same varying in surface contour and having a hardness differential whereby under the tension of the bolt, portions on the harder surfaces create counterpart interlocking impressions in the softer material, the interposed layer being of softer material than the end faces of the joined members and the interlock forming portions being shallow, sharp edged ridges on the end faces of the members.

5. A tension bolt joint comprising members having opposed abutment faces, a layer of shear load carrying material between said opposed abutment faces, said members having bolt seats in back of said abutment faces and registering oversize bolt passages extending between said seats, a bolt having a head bearing on one seat and a nut bearing on the other seat, the grip portion of the bolt between said head and nut extending free of engagement through said bolt passages, said intermediate shear load carrying layer and the opposing abutment faces at opposite sides of the same varying in surface contour and having a hardness differential whereby under the tension of the bolt, portions on the 25 harder surfaces create counterpart interlocking impressions in the softer material, said impression forming portions comprising spaced, projecting, shallow, sharp edged ridges.

6. A tension :bolt joint comprising members 30 2,206,223

having opposed abutment faces, a layer of shear load carrying material between said opposed abutment faces, said members having bolt seats in back of said abutment faces and registering oversize bolt passages extending between said seats, a bolt having a head bearing on one seat and a nut bearing on the other seat, the grip portion of the bolt between said head and nut extending free of engagement through said bolt passages, said intermediate shear load carrying layer and the opposing abutment faces at opposite sides of the same varying in surface contour and having a hardness differential Whereby under the tension of the bolt, portions on the harder surfaces create counterpart interlocking impressions in the softer material, said impression forming portions being in the form of ridges extending spirally about the axis of said bolt.

HAROLD W. EARHART.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,567,813 Oleson Dec. 29, 1925 1,834,581 Ferrell et al. Dec. 1, 1931 Dearborn July 2, 1940 

